content: // Protocol Buffers - Google's data interchange format
  // Copyright 2008 Google Inc.  All rights reserved.
  // https://developers.google.com/protocol-buffers/
  //
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  //
  //     * Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  //     * Redistributions in binary form must reproduce the above
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  // in the documentation and/or other materials provided with the
  // distribution.
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  // this software without specific prior written permission.
  //
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  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  package com.google.protobuf;
  
  /**
   * <p>An {@code RpcController} mediates a single method call.  The primary
   * purpose of the controller is to provide a way to manipulate settings
   * specific to the RPC implementation and to find out about RPC-level errors.
   *
   * <p>Starting with version 2.3.0, RPC implementations should not try to build
   * on this, but should instead provide code generator plugins which generate
   * code specific to the particular RPC implementation.  This way the generated
   * code can be more appropriate for the implementation in use and can avoid
   * unnecessary layers of indirection.
   *
   * <p>The methods provided by the {@code RpcController} interface are intended
   * to be a "least common denominator" set of features which we expect all
   * implementations to support.  Specific implementations may provide more
   * advanced features (e.g. deadline propagation).
   *
   * @author kenton@google.com Kenton Varda
   */
  public interface RpcController {
    // -----------------------------------------------------------------
    // These calls may be made from the client side only.  Their results
    // are undefined on the server side (may throw RuntimeExceptions).
  
    /**
     * Resets the RpcController to its initial state so that it may be reused in
     * a new call.  This can be called from the client side only.  It must not
     * be called while an RPC is in progress.
     */
    void reset();
  
    /**
     * After a call has finished, returns true if the call failed.  The possible
     * reasons for failure depend on the RPC implementation.  {@code failed()}
     * most only be called on the client side, and must not be called before a
     * call has finished.
     */
    boolean failed();
  
    /**
     * If {@code failed()} is {@code true}, returns a human-readable description
     * of the error.
     */
    String errorText();
  
    /**
     * Advises the RPC system that the caller desires that the RPC call be
     * canceled.  The RPC system may cancel it immediately, may wait awhile and
     * then cancel it, or may not even cancel the call at all.  If the call is
     * canceled, the "done" callback will still be called and the RpcController
     * will indicate that the call failed at that time.
     */
    void startCancel();
  
    // -----------------------------------------------------------------
    // These calls may be made from the server side only.  Their results
    // are undefined on the client side (may throw RuntimeExceptions).
  
    /**
     * Causes {@code failed()} to return true on the client side.  {@code reason}
     * will be incorporated into the message returned by {@code errorText()}.
     * If you find you need to return machine-readable information about
     * failures, you should incorporate it into your response protocol buffer
     * and should NOT call {@code setFailed()}.
     */
    void setFailed(String reason);
  
    /**
     * If {@code true}, indicates that the client canceled the RPC, so the server
     * may as well give up on replying to it.  This method must be called on the
     * server side only.  The server should still call the final "done" callback.
     */
    boolean isCanceled();
  
    /**
     * Asks that the given callback be called when the RPC is canceled.  The
     * parameter passed to the callback will always be {@code null}.  The
     * callback will always be called exactly once.  If the RPC completes without
     * being canceled, the callback will be called after completion.  If the RPC
     * has already been canceled when NotifyOnCancel() is called, the callback
     * will be called immediately.
     *
     * <p>{@code notifyOnCancel()} must be called no more than once per request.
     * It must be called on the server side only.
     */
    void notifyOnCancel(RpcCallback<Object> callback);
  }
  